The conventional process for leather tanning comprise the following operations: bating, pickling, pre-tanning and tanning.
The bating (purging or cleaning) of leather hides consists of deliming (removal of lime) and then bating the hides with enzymes. The second step is the pickling operation, where the bated hide is treated with sulfuric acid and sodium chloride in order to avoid, eliminate or reduce hide deterioration. Afterwards, the pre-tanning step is executed with chrome (chromic acid) or glutaraldehyde; this is the process that gives the hide its pretanning characteristics, allowing some operations, such as splitting, and afterwards, shawing the leather. This phase results in less steps with the use of a smaller quantity of chemicals. Finally the tanning of the hide is performed with chrome (chromic acid) and/or tannins, in accordance with the specifications to be reached.